1. Field of the Invention
The present invention relates to a molten metal supply system and, more particularly, a continuous pressure molten metal supply system and method for forming continuous metal articles of indefinite length.
2. Description of the Prior Art
The metal working process known as extrusion involves pressing metal stock (ingot or billet) through a die opening having a predetermined configuration in order to form a shape having a longer length and a substantially constant cross-section. For example, in the extrusion of aluminum alloys, the aluminum stock is preheated to the proper extrusion temperature. The aluminum stock is then placed into a heated cylinder. The cylinder utilized in the extrusion process has a die opening at one end of the desired shape and a reciprocal piston or ram having approximately the same cross-sectional dimensions as the bore of the cylinder. This piston or ram moves against the aluminum stock to compress the aluminum stock. The opening in the die is the path of least resistance for the aluminum stock under pressure. The aluminum stock deforms and flows through the die opening to produce an extruded product having the same cross-sectional shape as the die opening.
Referring to FIG. 1, the foregoing described extrusion process is identified by reference numeral 10, and typically consists of several discreet and discontinuous operations including: melting 20, casting 30, homogenizing 40, optionally sawing 50, reheating 60, and finally, extrusion 70. The aluminum stock is cast at an elevated temperature and typically cooled to room temperature. Because the aluminum stock is cast, there is a certain amount of inhomogeneity in the structure and the aluminum stock is heated to homogenize the cast metal. Following the homogenization step, the aluminum stock is cooled to room temperature. After cooling, the homogenized aluminum stock is reheated in a furnace to an elevated temperature called the preheat temperature. Those skilled in the art will appreciate that the preheat temperature is generally the same for each billet that is to be extruded in a series of billets and is based on experience. After the aluminum stock has reached the preheat temperature, it is ready to be placed in an extrusion press and extruded.
All of the foregoing steps relate to practices that are well known to those skilled in the art of casting and extruding. Each of the foregoing steps is related to metallurgical control of the metal to be extruded. These steps are very cost intensive, with energy costs incurring each time the metal stock is reheated from room temperature. There are also in-process recovery costs associated with the need to trim the metal stock, labor costs associated with process inventory, and capital and operational costs for the extrusion equipment.
Attempts have been made in the prior art to design an extrusion apparatus that will operate directly with molten metal. U.S. Pat. No. 3,328,994 to Lindemann discloses one such example. The Lindemann patent discloses an apparatus for extruding metal through an extrusion nozzle to form a solid rod. The apparatus includes a container for containing a supply of molten metal and an extrusion die (i.e., extrusion nozzle) located at the outlet of the container. A conduit leads from a bottom opening of the container to the extrusion nozzle. A heated chamber is located in the conduit leading from the bottom opening of the container to the extrusion nozzle and is used to heat the molten metal passing to the extrusion nozzle. A cooling chamber surrounds the extrusion nozzle to cool and solidify the molten metal as it passes therethrough. The container is pressurized to force the molten metal contained in the container through the outlet conduit, heated chamber and ultimately, the extrusion nozzle.
U.S. Pat. No. 4,075,881 to Kreidler discloses a method and device for making rods, tubes, and profiled articles directly from molten metal by extrusion through use of a forming tool and die. The molten metal is charged into a receiving compartment of the device in successive batches that are cooled so as to be transformed into a thermal-plastic condition. The successive batches build up layer-by-layer to form a bar or other similar article.
U.S. Pat. Nos. 4,774,997 and 4,718,476, both to Eibe, disclose an apparatus and method for continuous extrusion casting of molten metal. In the apparatus disclosed by the Eibe patents, molten metal is contained in a pressure vessel that may be pressurized with air or an inert gas such as argon. When the pressure vessel is pressurized, the molten metal contained therein is forced through an extrusion die assembly. The extrusion die assembly includes a mold that is in fluid communication with a downstream sizing die. Spray nozzles are positioned to spray water on the outside of the mold to cool and solidify the molten metal passing therethrough. The cooled and solidified metal is then forced through the sizing die. Upon exiting the sizing die, the extruded metal in the form of a metal strip is passed between a pair of pinch rolls and further cooled before being wound on a coiler.
An object of the present invention is to provide a molten metal supply system that may be used to supply molten metal to downstream metal-working or forming processes at substantially constant working pressures and flow rates. It is a further object of the present invention to provide a molten metal supply system and method capable of forming continuous metal articles of indefinite lengths.
The above objects are generally accomplished by a method of forming continuous metal articles of indefinite length as described herein. The method may generally include the steps of: providing a plurality of molten metal injectors each having an injector housing and a piston reciprocally operable within the housing, with the injectors each in fluid communication with a molten metal supply source and an outlet manifold, and with the piston of each of the injectors movable through a first stroke wherein molten metal is received into the respective housings from the molten metal supply source, and a second stroke wherein the injectors each provide molten metal to the outlet manifold under pressure, and wherein the outlet manifold includes a plurality of outlet dies for forming continuous metal articles of indefinite length, with the outlet dies configured to cool and solidify the molten metal to form the metal articles; serially actuating the injectors to move the respective pistons through their first and second strokes at different times to provide substantially constant molten metal flow rate and pressure to the outlet manifold; cooling the molten metal in the outlet dies to form semi-solid state metal in the respective outlet dies; solidifying the semi-state metal in the outlet dies to form solidified metal having an as-cast structure; discharging the solidified metal through outlet die apertures defined by the respective outlet dies to form the metal articles.
The method may include the step of working the solidified metal in the outlet dies to generate a wrought structure in the solidified metal before the step of discharging the solidified metal through the die apertures. The step of working the solidified metal in the outlet dies may be performed in a divergent-convergent chamber located upstream of the die aperture of each of the outlet dies.
The outlet dies may each include an outlet die passage communicating with the die aperture for conveying the metal to the die aperture. The die aperture may define a smaller cross sectional area than the die passage. The step of working the solidified metal may be performed by discharging the solidified metal through the smaller cross section die aperture of each of the outlet dies. At least one of the outlet dies may have a die passage defining a smaller cross sectional area than the corresponding die aperture. The step of working the solidified metal in the at least one outlet die may be performed by discharging the solidified metal from the smaller cross section die passage into the corresponding larger cross section die aperture.
The method may include the step of discharging the solidified metal of at least one of the metal articles through a second outlet die defining a die aperture. The second outlet die may be located downstream of the first outlet die. The second die aperture may define a smaller cross sectional area than the first die aperture. The method may then include the step of further working the solidified metal of the at least one metal article to form the wrought structure by discharging the solidified metal through the second die aperture.
The method may include the step of working the solidified metal forming at least one of the metal articles to generate wrought structure in the at least one metal article, with the working step occurring downstream of the outlet dies. The working step may be performed by a plurality of rolls in contact with the at least one metal article. The at least one metal article may be a continuous plate or continuous ingot.
The die aperture of at least one of the outlet dies may have a symmetrical cross section with respect to at least one axis passing threrethrough for forming a metal article having a symmetrical cross section. Additionally, the die aperture of at least one of the outlet dies may be configured to form a circular shaped cross section metal article. Further, the die aperture of at least one of the outlet dies may be configured to form a polygonal shaped cross section metal article. The die aperture of at least one of the outlet dies may also be configured to form an annular shaped cross section metal article. Furthermore, the die aperture of at least one of the outlet dies may have an asymmetrical cross section for forming a metal article having an asymmetrical cross section.
The die aperture of at least one of the outlet dies may have a symmetrical cross section with respect to at least one axis passing threrethrough for forming a metal article having a symmetrical cross section, and the die aperture of at least one of the outlet dies may have an asymmetrical cross section for forming a metal article having an asymmetrical cross section.
A plurality of rolls may be associated with each of the outlet dies and in contact with the formed metal articles downstream of the respective die apertures. The method may then further include the step of providing backpressure to the plurality of injectors through frictional contact between the rolls and metal articles. At least one of the die apertures is preferably configured to form a continuous plate. The method may then also include the step of further working the solidified metal forming the continuous plate with the rolls to generate the wrought structure.
The outlet dies may each include an outlet die passage communicating with the die aperture for conveying the metal to the die aperture. At least one of the outlet dies may have a die passage defining a smaller cross sectional area than the corresponding die aperture, so that the method may include the step of working the solidified metal to generate wrought structure by discharging the solidified metal from the smaller cross section die passage into the corresponding larger cross section die aperture of the at least one outlet die. The larger cross section die aperture may be configured to form a continuous ingot. A plurality of rolls may be in contact with the ingot downstream of the at least one outlet die, so that the method may further including the step of providing backpressure to the plurality of injectors through frictional contact between the rolls and ingot. The method may further include the step of further working the solidified metal forming the ingot with the rolls to generate the wrought structure.
The metal articles formed by the foregoing described method make take any of the following shapes, however the present method is not limited to the following listed shapes: a solid rod having a polygonal or circular shaped cross section; a circular or polygonal shaped cross section tube; a plate having a polygonal shaped cross section; and ingot having a polygonal or circular shaped cross section.
The present invention is also an apparatus for forming continuous metal articles of indefinite length. The apparatus includes an outlet manifold and a plurality of outlet dies. The outlet manifold is configured for fluid communication with a source of molten metal. The plurality of outlet dies is in fluid communication with the outlet manifold. The outlet dies are configured to form a plurality of continuous metal articles of indefinite length. The outlet dies are each further comprised of a die housing attached to the outlet manifold. The die housing defines a die aperture configured to form the cross sectional shape of the continuous metal article exiting the outlet die. The die housing also defines a die passage in fluid communication with the outlet manifold for conveying metal to the outlet die aperture. Additionally, the die housing defines a coolant chamber surrounding at least a portion of the die passage for cooling and solidifying molten metal received from the outlet manifold and passing through the die passage to the die aperture.
The die passage of at least one of the outlet dies may define a divergent-convergent located upstream of the corresponding die aperture. The die passage of at least one of the outlet dies may include a mandrel positioned therein to form an annular shaped cross section metal article. A plurality of rolls may be associated with each of the outlet dies and positioned to contact the formed metal articles downstream of the respective die apertures for frictionally engaging the metal articles and apply backpressure to the molten metal in the manifold.
At least one of the die passages of the outlet dies may define a larger cross sectional area than the cross sectional area defined by the corresponding die aperture. At least one of the die passages may define a smaller cross sectional area than the cross sectional area defined by the corresponding die aperture.
The die passage of at least one of the outlet dies may define a larger cross sectional area than the cross sectional area defined by the corresponding die aperture. A second outlet die may be located downstream of the at least one outlet die. The second outlet die may define a die aperture having a smaller cross sectional area than the corresponding upstream die aperture. The second outlet die may be fixedly attached to the upstream outlet die.
The die housing of each of the outlet dies may be fixedly attached to the outlet manifold. Additionally, the die housing of each of the outlet dies may be integrally formed with the outlet manifold.
The die aperture of at least one of the outlet dies may be configured to form a circular shaped cross section metal article. In additional, the die aperture of at least one of the outlet dies may be configured to form a polygonal shaped cross section metal article. Further, the die aperture of at least one of the outlet dies may be configured to form an annular shaped cross section metal article. The die aperture of at least one of the outlet dies may have an asymmetrical cross section for forming a metal article having an asymmetrical cross section. Furthermore, the die aperture of at least one of the outlet dies may have a symmetrical cross section with respect to at least one axis passing threrethrough for forming a metal article having a symmetrical cross section.
The die aperture of at least one of the outlet dies may be configured to form a continuous plate or a continuous ingot. The continuous ingot may have a polygonal shaped or circular shaped cross section. The continuous plate may also have a polygonal shaped cross section.
The apparatus may further include a single outlet die having a die housing defining a die aperture and a die passage in fluid communication with the outlet manifold. The die housing may further define a coolant chamber at least partially surrounding the die passage. The die aperture is preferably configured to form the cross sectional shape of the continuous metal article.
Further details and advantages of the present invention will become apparent from the following detailed description read in conjunction with the drawings, wherein like parts are designated with like reference numerals.